Question 1

How do I test a regular expression?

Accepted Answer

Enter your regex pattern in the pattern field, add flags (g for global, i for case-insensitive), and input your test string. Matches are highlighted in yellow instantly. View match details including position and capture groups.

Question 2

What are regex flags?

Accepted Answer

Flags modify regex behavior: g (global) finds all matches, i (case-insensitive) ignores case, m (multiline) makes ^ and $ match line boundaries, s (dotall) lets . match newlines, u (unicode) enables unicode features. Combine flags like 'gi' for multiple effects.

Question 3

How do capture groups work?

Accepted Answer

Parentheses () create capture groups that extract parts of matches. For phone (\d{3})-(\d{3})-(\d{4}), groups capture area code, prefix, line number. Named groups (?<name>...) give groups names. Non-capture groups (?:...) group without capturing.

Question 4

What regex patterns match email addresses?

Accepted Answer

Simple: \b\w+@\w+\.\w+\b matches basic emails. Complex: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,} handles most real emails. Full RFC-compliant regex is extremely long. For validation, prefer simple patterns or dedicated validators.

Question 5

Why do developers need regex testers?

Accepted Answer

Regex testers help developers: debug patterns before deploying, visualize matches to verify behavior, learn regex syntax with examples, test edge cases and special characters, validate input patterns for forms. Essential tool for text processing, validation, and parsing.

Regex Tester

Match Results (5 found)

Quick Examples

Regex Reference